1. Field of the Invention
The present invention relates to an optical film, a polarizing plate using the optical film, and a liquid crystal display device having the optical film.
2. Description of the Related Art
There has been known a liquid crystal display device equipped with a liquid crystal cell containing rod-shaped liquid crystalline molecules, and a pair of polarizing plates sandwiching therein the liquid crystal cell. Polarizing plates of this type liquid crystal display device are each provided with an optical film for adjusting a phase difference of light passed through the liquid crystal cell, i.e., for optical compensation.
As an optical film, for example, there have been known an optical film in which an optically anisotropic layer containing a liquid crystal compound, such as a discotic compound, is stacked over a support excellent in optical transmission and optical isotropy, such as triacetylcellulose.
This type of optical film has a phase difference which differs on a wavelength-to-wavelength basis of transmission light, and usually, has wavelength dispersibility.
The wavelength dispersibility of an optical film has an influence on the display properties of a liquid crystal display device, such as color tint. Therefore, there have been attempts to develop optical films capable of improving display properties of liquid crystal display devices.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2006-208604 proposes an optical film in which a birefringent film is stacked over an optically anisotropic layer formed of a polymer film such as cycloolefin-based polymer.
The birefringent film is said to have a relationship between in-plane retardation value Re (λ) and wavelength λ (nm) of Re (450)/Re (550)>1.08.
Also, the optical film is formed so that a slow axis of an optically anisotropic layer is substantially orthogonal to a slow axis of the birefringent film.
Japanese Patent Application Laid-Open (JP-A) No. 2007-298960 proposes an optical film having a transparent protective layer which has a plane phase difference value of 0.97 or more and less than 1.03 (0.97<R (450 nm)/R (550 nm)<1.03).
Japanese Patent Application Laid-Open (JP-A) No. 2007-298960 discloses to use as an optical film a resin film exhibiting so-called reverse wavelength dispersibility in which as the wavelength is longer, the phase difference is greater.
JP-A Nos. 2006-208604 and 2007-298960, however, do not disclose nor suggest that it is possible to improve all of the contrast, color tint and bilateral symmetry property of a liquid crystal display device by use of an optical film in which, among optically anisotropic layers other than the optically anisotropic layer containing a liquid crystal compound, an optically anisotropic layer that exhibits wavelength dispersibility satisfying the following Expression (1) and an optically anisotropic layer that exhibits wavelength dispersibility satisfying the following Expression (2) are laminated so that slow axes thereof are parallel to each other.0≦Re(450)/Re(550)≦0.5  Expression (1)0.95≦Re(450)/Re(550)≦1.05  Expression (2)